CNDP1 and diabetes mellitus: Serum CN-1 concentrations in patients with or without DKD were significantly higher than that of the controls and among the patients with diabetes lower in the DKD group (CON vs. no-DKD vs. DKD: 0.55 ± 0.03 vs. 0.86 ± 0.04 vs. 0.74 ± 0.04 ng/ml).